path: root/gcc/profile.c

/* Calculate branch probabilities, and basic block execution counts. 
   Copyright (C) 1990, 91-94, 96-99, 2000 Free Software Foundation, Inc.
   Contributed by James E. Wilson, UC Berkeley/Cygnus Support;
   based on some ideas from Dain Samples of UC Berkeley.
   Further mangling by Bob Manson, Cygnus Support.

This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* ??? Register allocation should use basic block execution counts to
   give preference to the most commonly executed blocks.  */

/* ??? The .da files are not safe.  Changing the program after creating .da
   files or using different options when compiling with -fbranch-probabilities
   can result the arc data not matching the program.  Maybe add instrumented
   arc count to .bbg file?  Maybe check whether PFG matches the .bbg file?  */

/* ??? Should calculate branch probabilities before instrumenting code, since
   then we can use arc counts to help decide which arcs to instrument.  */

#include "config.h"
#include "system.h"
#include "rtl.h"
#include "tree.h"
#include "flags.h"
#include "insn-flags.h"
#include "insn-config.h"
#include "output.h"
#include "regs.h"
#include "expr.h"
#include "function.h"
#include "gcov-io.h"
#include "toplev.h"
#include "ggc.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "defaults.h"

/* Additional information about the edges we need.  */
struct edge_info
  {
    unsigned int count_valid : 1;
    unsigned int on_tree : 1;
    unsigned int ignore : 1;
  };
struct bb_info
  {
    unsigned int count_valid : 1;
    int succ_count;
    int pred_count;
  };

#define EDGE_INFO(e)  ((struct edge_info *) (e)->aux)
#define BB_INFO(b)  ((struct bb_info *) (b)->aux)

/* Keep all basic block indexes nonnegative in the gcov output.  Index 0
   is used for entry block, last block exit block.   */
#define GCOV_INDEX_TO_BB(i)  ((i) == 0 ? ENTRY_BLOCK_PTR		\
    			      : (((i) == n_basic_blocks + 1)		\
			         ? EXIT_BLOCK_PTR : BASIC_BLOCK ((i)-1)))
#define BB_TO_GCOV_INDEX(bb)  ((bb) == ENTRY_BLOCK_PTR ? 0 		\
  			       : ((bb) == EXIT_BLOCK_PTR		\
				  ? n_basic_blocks + 1 : (bb)->index + 1))

/* Name and file pointer of the output file for the basic block graph.  */

static FILE *bbg_file;

/* Name and file pointer of the input file for the arc count data.  */

static FILE *da_file;

/* Pointer of the output file for the basic block/line number map. */
static FILE *bb_file;

/* Last source file name written to bb_file. */

static char *last_bb_file_name;

/* Used by final, for allocating the proper amount of storage for the
   instrumented arc execution counts.  */

int count_instrumented_edges;

/* Collect statistics on the performance of this pass for the entire source
   file.  */

static int total_num_blocks;
static int total_num_edges;
static int total_num_edges_instrumented;
static int total_num_blocks_created;
static int total_num_passes;
static int total_num_times_called;
static int total_hist_br_prob[20];
static int total_num_never_executed;
static int total_num_branches;

/* Forward declarations.  */
static void find_spanning_tree PARAMS ((struct edge_list *));
static void init_edge_profiler PARAMS ((void));
static rtx gen_edge_profiler PARAMS ((int));
static void instrument_edges PARAMS ((struct edge_list *));
static void output_gcov_string PARAMS ((const char *, long));
static void compute_branch_probabilities PARAMS ((void));
static basic_block find_group PARAMS ((basic_block));
static void union_groups PARAMS ((basic_block, basic_block));

/* If non-zero, we need to output a constructor to set up the
   per-object-file data. */
static int need_func_profiler = 0;

/* Add edge instrumentation code to the entire insn chain.

   F is the first insn of the chain.
   NUM_BLOCKS is the number of basic blocks found in F.  */

static void
instrument_edges (el)
     struct edge_list *el;
{
  int i;
  int num_instr_edges = 0;
  int num_edges = NUM_EDGES (el);
  remove_fake_edges ();

  for (i = 0; i < n_basic_blocks + 2; i++)
    {
      basic_block bb = GCOV_INDEX_TO_BB (i);
      edge e = bb->succ;
      while (e)
	{
	  struct edge_info *inf = EDGE_INFO (e);
	  if (!inf->ignore && !inf->on_tree)
	    {
	      if (e->flags & EDGE_ABNORMAL)
		abort ();
	      if (rtl_dump_file)
		fprintf (rtl_dump_file, "Edge %d to %d instrumented%s\n",
			 e->src->index, e->dest->index,
			 e->flags & EDGE_CRITICAL ? " (and split)" : "");
	      need_func_profiler = 1;
	      insert_insn_on_edge (
			 gen_edge_profiler (total_num_edges_instrumented
					    + num_instr_edges++), e);
	    }
	  e = e->succ_next;
	}
    }

  total_num_edges_instrumented += num_instr_edges;
  count_instrumented_edges = total_num_edges_instrumented;

  total_num_blocks_created += num_edges;
  if (rtl_dump_file)
    fprintf (rtl_dump_file, "%d edges instrumented\n", num_instr_edges);

  commit_edge_insertions ();
}

/* Output STRING to bb_file, surrounded by DELIMITER.  */

static void
output_gcov_string (string, delimiter)
     const char *string;
     long delimiter;
{
  long temp;
			
  /* Write a delimiter to indicate that a file name follows.  */
  __write_long (delimiter, bb_file, 4);

  /* Write the string.  */
  temp = strlen (string) + 1;
  fwrite (string, temp, 1, bb_file);

  /* Append a few zeros, to align the output to a 4 byte boundary.  */
  temp = temp & 0x3;
  if (temp)
    {
      char c[4];

      c[0] = c[1] = c[2] = c[3] = 0;
      fwrite (c, sizeof (char), 4 - temp, bb_file);
    }

  /* Store another delimiter in the .bb file, just to make it easy to find
     the end of the file name.  */
  __write_long (delimiter, bb_file, 4);
}


/* Compute the branch probabilities for the various branches.
   Annotate them accordingly.  */

static void
compute_branch_probabilities ()
{
  int i;
  int num_edges = 0;
  int changes;
  int passes;
  int hist_br_prob[20];
  int num_never_executed;
  int num_branches;
  int bad_counts = 0;
  struct bb_info *bb_infos;

  /* Attach extra info block to each bb.  */

  bb_infos = (struct bb_info *)
    xcalloc (n_basic_blocks + 2, sizeof (struct bb_info));
  for (i = 0; i < n_basic_blocks + 2; i++)
    {
      basic_block bb = GCOV_INDEX_TO_BB (i);
      edge e;

      bb->aux = &bb_infos[i];
      for (e = bb->succ; e; e = e->succ_next)
	if (!EDGE_INFO (e)->ignore)
	  BB_INFO (bb)->succ_count++;
      for (e = bb->pred; e; e = e->pred_next)
	if (!EDGE_INFO (e)->ignore)
	  BB_INFO (bb)->pred_count++;
    }

  /* Avoid predicting entry on exit nodes.  */
  BB_INFO (EXIT_BLOCK_PTR)->succ_count = 2;
  BB_INFO (ENTRY_BLOCK_PTR)->pred_count = 2;

  /* For each edge not on the spanning tree, set its execution count from
     the .da file.  */

  /* The first count in the .da file is the number of times that the function
     was entered.  This is the exec_count for block zero.  */

  for (i = 0; i < n_basic_blocks + 2; i++)
    {
      basic_block bb = GCOV_INDEX_TO_BB (i);
      edge e;
      for (e = bb->succ; e; e = e->succ_next)
	if (!EDGE_INFO (e)->ignore && !EDGE_INFO (e)->on_tree)
	  {
	    num_edges++;
	    if (da_file)
	      {
		long value;
		__read_long (&value, da_file, 8);
		e->count = value;
	      }
	    else
	      e->count = 0;
	    EDGE_INFO (e)->count_valid = 1;
	    BB_INFO (bb)->succ_count--;
	    BB_INFO (e->dest)->pred_count--;
	  }
    }

  if (rtl_dump_file)
    fprintf (rtl_dump_file, "%d edge counts read\n", num_edges);

  /* For every block in the file,
     - if every exit/entrance edge has a known count, then set the block count
     - if the block count is known, and every exit/entrance edge but one has
     a known execution count, then set the count of the remaining edge

     As edge counts are set, decrement the succ/pred count, but don't delete
     the edge, that way we can easily tell when all edges are known, or only
     one edge is unknown.  */

  /* The order that the basic blocks are iterated through is important.
     Since the code that finds spanning trees starts with block 0, low numbered
     edges are put on the spanning tree in preference to high numbered edges.
     Hence, most instrumented edges are at the end.  Graph solving works much
     faster if we propagate numbers from the end to the start.

     This takes an average of slightly more than 3 passes.  */

  changes = 1;
  passes = 0;
  while (changes)
    {
      passes++;
      changes = 0;
      for (i = n_basic_blocks + 1; i >= 0; i--)
	{
	  basic_block bb = GCOV_INDEX_TO_BB (i);
	  struct bb_info *bi = BB_INFO (bb);
	  if (! bi->count_valid)
	    {
	      if (bi->succ_count == 0)
		{
		  edge e;
		  int total = 0;

		  for (e = bb->succ; e; e = e->succ_next)
		    total += e->count;
		  bb->count = total;
		  bi->count_valid = 1;
		  changes = 1;
		}
	      else if (bi->pred_count == 0)
		{
		  edge e;
		  int total = 0;

		  for (e = bb->pred; e; e = e->pred_next)
		    total += e->count;
		  bb->count = total;
		  bi->count_valid = 1;
		  changes = 1;
		}
	    }
	  if (bi->count_valid)
	    {
	      if (bi->succ_count == 1)
		{
		  edge e;
		  int total = 0;

		  /* One of the counts will be invalid, but it is zero,
		     so adding it in also doesn't hurt.  */
		  for (e = bb->succ; e; e = e->succ_next)
		    total += e->count;

		  /* Seedgeh for the invalid edge, and set its count.  */
		  for (e = bb->succ; e; e = e->succ_next)
		    if (! EDGE_INFO (e)->count_valid && ! EDGE_INFO (e)->ignore)
		      break;

		  /* Calculate count for remaining edge by conservation.  */
		  total = bb->count - total;

		  if (! e)
		    abort ();
		  EDGE_INFO (e)->count_valid = 1;
		  e->count = total;
		  bi->succ_count--;
		  
		  BB_INFO (e->dest)->pred_count--;
		  changes = 1;
		}
	      if (bi->pred_count == 1)
		{
		  edge e;
		  int total = 0;

		  /* One of the counts will be invalid, but it is zero,
		     so adding it in also doesn't hurt.  */
		  for (e = bb->pred; e; e = e->pred_next)
		    total += e->count;

		  /* Seedgeh for the invalid edge, and set its count.  */
		  for (e = bb->pred; e; e = e->pred_next)
		    if (! EDGE_INFO (e)->count_valid && ! EDGE_INFO (e)->ignore)
		      break;

		  /* Calculate count for remaining edge by conservation.  */
		  total = bb->count - total + e->count;

		  if (! e)
		    abort ();
		  EDGE_INFO (e)->count_valid = 1;
		  e->count = total;
		  bi->pred_count--;
		  
		  BB_INFO (e->src)->succ_count--;
		  changes = 1;
		}
	    }
	}
    }
  if (rtl_dump_file)
    dump_flow_info (rtl_dump_file);

  total_num_passes += passes;
  if (rtl_dump_file)
    fprintf (rtl_dump_file, "Graph solving took %d passes.\n\n", passes);

  /* If the graph has been correctly solved, every block will have a
     succ and pred count of zero.  */
  for (i = 0; i < n_basic_blocks; i++)
    {
      basic_block bb = BASIC_BLOCK (i);
      if (BB_INFO (bb)->succ_count || BB_INFO (bb)->pred_count)
	abort ();
    }

  /* For every edge, calculate its branch probability and add a reg_note
     to the branch insn to indicate this.  */

  for (i = 0; i < 20; i++)
    hist_br_prob[i] = 0;
  num_never_executed = 0;
  num_branches = 0;

  for (i = 0; i < n_basic_blocks; i++)
    {
      basic_block bb = BASIC_BLOCK (i);
      edge e;
      rtx insn;
      int total;
      rtx note;

      total = bb->count;
      if (!total)
	continue;
      for (e = bb->succ; e; e = e->succ_next)
	{
	  if (any_condjump_p (e->src->end)
	      && !EDGE_INFO (e)->ignore
	      && !(e->flags & (EDGE_ABNORMAL | EDGE_ABNORMAL_CALL | EDGE_FAKE)))
	    {
	      int prob;
	      /* This calculates the branch probability as an integer between
		 0 and REG_BR_PROB_BASE, properly rounded to the nearest
		 integer.  Perform the arithmetic in double to avoid
		 overflowing the range of ints.  */
	      if (total == 0)
		prob = -1;
	      else
		{
		  prob = (((double)e->count * REG_BR_PROB_BASE)
			  + (total >> 1)) / total;
		  if (prob < 0 || prob > REG_BR_PROB_BASE)
		    {
		      if (rtl_dump_file)
			fprintf (rtl_dump_file, "bad count: prob for %d-%d thought to be %d (forcibly normalized)\n",
				 e->src->index, e->dest->index, prob);

		      bad_counts = 1;
		      prob = REG_BR_PROB_BASE / 2;
		    }
		  
		  /* Match up probability with JUMP pattern.  */
		  if (e->flags & EDGE_FALLTHRU)
		    prob = REG_BR_PROB_BASE - prob;
		}
	      
	      if (prob == -1)
		num_never_executed++;
	      else
		{
		  int index = prob * 20 / REG_BR_PROB_BASE;
		  if (index == 20)
		    index = 19;
		  hist_br_prob[index]++;
		}
	      num_branches++;
	      
	      note = find_reg_note (e->src->end, REG_BR_PROB, 0);
	      /* There may be already note put by some other pass, such
	         as builtin_expect expander.  */
	      if (note)
		XEXP (note, 0) = GEN_INT (prob);
	      else
		REG_NOTES (e->src->end)
		  = gen_rtx_EXPR_LIST (REG_BR_PROB, GEN_INT (prob),
				       REG_NOTES (e->src->end));
	    }
	}

      /* Add a REG_EXEC_COUNT note to the first instruction of this block.  */
      insn = next_nonnote_insn (bb->head);

      if (GET_CODE (bb->head) == CODE_LABEL)
	insn = next_nonnote_insn (insn);

      /* Avoid crash on empty basic blocks.  */
      if (insn && INSN_P (insn))
	REG_NOTES (insn)
	  = gen_rtx_EXPR_LIST (REG_EXEC_COUNT, GEN_INT (total),
			       REG_NOTES (insn));
    }
  
  /* This should never happen.  */
  if (bad_counts)
    warning ("Arc profiling: some edge counts were bad.");

  if (rtl_dump_file)
    {
      fprintf (rtl_dump_file, "%d branches\n", num_branches);
      fprintf (rtl_dump_file, "%d branches never executed\n",
	       num_never_executed);
      if (num_branches)
	for (i = 0; i < 10; i++)
	  fprintf (rtl_dump_file, "%d%% branches in range %d-%d%%\n",
		   (hist_br_prob[i] + hist_br_prob[19-i]) * 100 / num_branches,
		   5 * i, 5 * i + 5);

      total_num_branches += num_branches;
      total_num_never_executed += num_never_executed;
      for (i = 0; i < 20; i++)
	total_hist_br_prob[i] += hist_br_prob[i];

      fputc ('\n', rtl_dump_file);
      fputc ('\n', rtl_dump_file);
    }

  free (bb_infos);
}

/* Instrument and/or analyze program behavior based on program flow graph.
   In either case, this function builds a flow graph for the function being
   compiled.  The flow graph is stored in BB_GRAPH.

   When FLAG_PROFILE_ARCS is nonzero, this function instruments the edges in
   the flow graph that are needed to reconstruct the dynamic behavior of the
   flow graph.

   When FLAG_BRANCH_PROBABILITIES is nonzero, this function reads auxiliary
   information from a data file containing edge count information from previous
   executions of the function being compiled.  In this case, the flow graph is
   annotated with actual execution counts, which are later propagated into the
   rtl for optimization purposes.

   Main entry point of this file.  */

void
branch_prob ()
{
  int i;
  int num_edges;
  struct edge_info *edge_infos;
  struct edge_list *el;

  /* Start of a function.  */
  if (flag_test_coverage)
    output_gcov_string (current_function_name, (long) -2);

  total_num_times_called++;

  /* We can't handle cyclic regions constructed using abnormal edges.
     To avoid these we replace every source of abnormal edge by a fake
     edge from entry node and every destination by fake edge to exit.
     This keeps graph acyclic and our calculation exact for all normal
     edges except for exit and entrance ones.
   
     We also add fake exit edges for each call and asm statement in the
     basic, since it may not return.  */

  for (i = 0; i < n_basic_blocks ; i++)
    {
      rtx insn;
      int need_exit_edge = 0, need_entry_edge = 0;
      int have_exit_edge = 0, have_entry_edge = 0;
      basic_block bb = BASIC_BLOCK (i);
      edge e;

      for (e = bb->succ; e; e = e->succ_next)
	{
	  if ((e->flags & (EDGE_ABNORMAL | EDGE_ABNORMAL_CALL))
	       && e->dest != EXIT_BLOCK_PTR)
	    need_exit_edge = 1;
	  if (e->dest == EXIT_BLOCK_PTR)
	    have_exit_edge = 1;
	}
      for (e = bb->pred; e; e = e->pred_next)
	{
	  if ((e->flags & (EDGE_ABNORMAL | EDGE_ABNORMAL_CALL))
	       && e->src != ENTRY_BLOCK_PTR)
	    need_entry_edge = 1;
	  if (e->src == ENTRY_BLOCK_PTR)
	    have_entry_edge = 1;
	}

      /* ??? Not strictly needed unless flag_test_coverage, but adding
	 them anyway keeps the .da file consistent.  */
      /* ??? Currently inexact for basic blocks with multiple calls. 
	 We need to split blocks here.  */
      for (insn = bb->head;
	   insn != NEXT_INSN (bb->end);
	   insn = NEXT_INSN (insn))
	{
	  rtx set;
	  if (GET_CODE (insn) == CALL_INSN && !CONST_CALL_P (insn))
	    need_exit_edge = 1;
	  else if (GET_CODE (insn) == INSN)
	    {
	      set = PATTERN (insn);
	      if (GET_CODE (set) == PARALLEL)
		set = XVECEXP (set, 0, 0);
	      if ((GET_CODE (set) == ASM_OPERANDS && MEM_VOLATILE_P (set))
		  || GET_CODE (set) == ASM_INPUT)
		need_exit_edge = 1;
	    }
	}

      if (need_exit_edge && !have_exit_edge)
	{
	  if (rtl_dump_file)
	    fprintf (rtl_dump_file, "Adding fake exit edge to bb %i\n",
		     bb->index);
          make_edge (NULL, bb, EXIT_BLOCK_PTR, EDGE_FAKE);
	}
      if (need_entry_edge && !have_entry_edge)
	{
	  if (rtl_dump_file)
	    fprintf (rtl_dump_file, "Adding fake entry edge to bb %i\n",
		     bb->index);
          make_edge (NULL, ENTRY_BLOCK_PTR, bb, EDGE_FAKE);
	}
    }

  el = create_edge_list ();
  num_edges = NUM_EDGES (el);
  edge_infos = (struct edge_info *)
    xcalloc (num_edges, sizeof (struct edge_info));

  for (i = 0 ; i < num_edges ; i++)
    {
      edge e = INDEX_EDGE (el, i);
      e->count = 0;
      e->aux = &edge_infos[i];

      /* Mark edges we've replaced by fake edges above as ignored.  */
      if ((e->flags & (EDGE_ABNORMAL | EDGE_ABNORMAL_CALL))
	  && e->src != ENTRY_BLOCK_PTR && e->dest != EXIT_BLOCK_PTR)
	EDGE_INFO (e)->ignore = 1;
    }

  total_num_blocks += n_basic_blocks + 2;
  if (rtl_dump_file)
    fprintf (rtl_dump_file, "%d basic blocks\n", n_basic_blocks);

  total_num_edges += num_edges;
  if (rtl_dump_file)
    fprintf (rtl_dump_file, "%d edges\n", num_edges);

#ifdef ENABLE_CHECKING
  verify_flow_info ();
#endif

  /* Output line number information about each basic block for
     GCOV utility.  */
  if (flag_test_coverage)
    {
      int i = 0;
      for (i = 0 ; i < n_basic_blocks; i++)
        {
	  basic_block bb = BASIC_BLOCK (i);
	  rtx insn = bb->head;
          static int ignore_next_note = 0;

	  /* We are looking for line number notes.  Search backward before
	     basic block to find correct ones.  */
	  insn = prev_nonnote_insn (insn);
	  if (!insn)
	    insn = get_insns ();
	  else
	    insn = NEXT_INSN (insn);

	  /* Output a zero to the .bb file to indicate that a new
	     block list is starting.  */
	  __write_long (0, bb_file, 4);

	  while (insn != bb->end)
	    {
	      if (GET_CODE (insn) == NOTE)
		{
		  /* Must ignore the line number notes that immediately
		     follow the end of an inline function to avoid counting
		     it twice.  There is a note before the call, and one
		     after the call.  */
		  if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_REPEATED_LINE_NUMBER)
		    ignore_next_note = 1;
		  else if (NOTE_LINE_NUMBER (insn) > 0)
		    {
		      if (ignore_next_note)
			ignore_next_note = 0;
		      else
			{
			  /* If this is a new source file, then output the
			     file's name to the .bb file.  */
			  if (! last_bb_file_name
			      || strcmp (NOTE_SOURCE_FILE (insn),
					 last_bb_file_name))
			    {
			      if (last_bb_file_name)
				free (last_bb_file_name);
			      last_bb_file_name
				= xstrdup (NOTE_SOURCE_FILE (insn));
			      output_gcov_string (NOTE_SOURCE_FILE (insn),
						  (long)-1);
			    }
			  /* Output the line number to the .bb file.  Must be
			     done after the output_bb_profile_data() call, and
			     after the file name is written, to ensure that it
			     is correctly handled by gcov.  */
			  __write_long (NOTE_LINE_NUMBER (insn), bb_file, 4);
			}
		    }
		}
	      insn = NEXT_INSN (insn);
	    }
        }
      __write_long (0, bb_file, 4);
    }

  /* Create spanning tree from basic block graph, mark each edge that is
     on the spanning tree.  We insert as many abnormal and critical edges
     as possible to minimize number of edge splits necesary. */

  find_spanning_tree (el);

  /* Create a .bbg file from which gcov can reconstruct the basic block
     graph.  First output the number of basic blocks, and then for every
     edge output the source and target basic block numbers.
     NOTE: The format of this file must be compatible with gcov.  */

  if (flag_test_coverage)
    {
      int flag_bits;

      /* The plus 2 stands for entry and exit block.  */
      __write_long (n_basic_blocks + 2, bbg_file, 4);
      __write_long (num_edges + 1, bbg_file, 4);

      for (i = 0; i < n_basic_blocks + 1; i++)
	{
	  basic_block bb = GCOV_INDEX_TO_BB (i);
	  edge e;
	  long count = 0;

	  for (e = bb->succ; e; e = e->succ_next)
	    if (!EDGE_INFO (e)->ignore)
	      count++;
	  __write_long (count, bbg_file, 4);

	  for (e = bb->succ; e; e = e->succ_next)
	    {
	      struct edge_info *i = EDGE_INFO (e);
	      if (!i->ignore)
		{
		  flag_bits = 0;
		  if (i->on_tree)
		    flag_bits |= 0x1;
		  if (e->flags & EDGE_ABNORMAL)
		    flag_bits |= 0x2;
		  if (e->flags & EDGE_FALLTHRU)
		    flag_bits |= 0x4;

		  __write_long (BB_TO_GCOV_INDEX (e->dest), bbg_file, 4);
		  __write_long (flag_bits, bbg_file, 4);
	        }
	    }
	}
      /* Emit fake loopback edge for EXIT block to maitain compatibility with
         old gcov format.  */
      __write_long (1, bbg_file, 4);
      __write_long (0, bbg_file, 4);
      __write_long (0x1, bbg_file, 4);

      /* Emit a -1 to separate the list of all edges from the list of
	 loop back edges that follows.  */
      __write_long (-1, bbg_file, 4);
    }

  if (flag_branch_probabilities)
    compute_branch_probabilities ();

  /* For each edge not on the spanning tree, add counting code as rtl.  */

  if (profile_arc_flag)
    {
      instrument_edges (el);
      allocate_reg_info (max_reg_num (), FALSE, FALSE);
    }

  remove_fake_edges ();
  free (edge_infos);
  free_edge_list (el);
}

/* Union find algorithm implementation for the basic blocks using
   aux fields. */

static basic_block
find_group (bb)
     basic_block bb;
{
  basic_block group = bb, bb1;

  while ((basic_block) group->aux != group)
    group = (basic_block) group->aux;

  /* Compress path.  */
  while ((basic_block) bb->aux != group)
    {
      bb1 = (basic_block) bb->aux;
      bb->aux = (void *) group;
      bb = bb1;
    }
  return group;
}

static void
union_groups (bb1, bb2)
     basic_block bb1, bb2;
{
  basic_block bb1g = find_group (bb1);
  basic_block bb2g = find_group (bb2);

  /* ??? I don't have a place for the rank field.  OK.  Lets go w/o it,
     this code is unlikely going to be performance problem anyway.  */
  if (bb1g == bb2g)
    abort ();

  bb1g->aux = bb2g;
}

/* This function searches all of the edges in the program flow graph, and puts
   as many bad edges as possible onto the spanning tree.  Bad edges include
   abnormals edges, which can't be instrumented at the moment.  Since it is
   possible for fake edges to form an cycle, we will have to develop some
   better way in the future.  Also put critical edges to the tree, since they
   are more expensive to instrument.  */

static void
find_spanning_tree (el)
     struct edge_list *el;
{
  int i;
  int num_edges = NUM_EDGES (el);

  /* We use aux field for standard union-find algorithm.  */
  EXIT_BLOCK_PTR->aux = EXIT_BLOCK_PTR;
  ENTRY_BLOCK_PTR->aux = ENTRY_BLOCK_PTR;
  for (i = 0; i < n_basic_blocks; i++)
    BASIC_BLOCK (i)->aux = BASIC_BLOCK (i);

  /* Add fake edge exit to entry we can't instrument.  */
  union_groups (EXIT_BLOCK_PTR, ENTRY_BLOCK_PTR);

  /* First add all abnormal edges to the tree unless they form an cycle.  */
  for (i = 0; i < num_edges; i++)
    {
      edge e = INDEX_EDGE (el, i);
      if ((e->flags & (EDGE_ABNORMAL | EDGE_ABNORMAL_CALL | EDGE_FAKE))
	  && !EDGE_INFO (e)->ignore
	  && (find_group (e->src) != find_group (e->dest)))
	{
	  EDGE_INFO (e)->on_tree = 1;
	  union_groups (e->src, e->dest);
	}
    }

  /* Now insert all critical edges to the tree unless they form an cycle.  */
  for (i = 0; i < num_edges; i++)
    {
      edge e = INDEX_EDGE (el, i);
      if ((e->flags & EDGE_CRITICAL)
	  && !EDGE_INFO (e)->ignore
	  && (find_group (e->src) != find_group (e->dest)))
	{
	  EDGE_INFO (e)->on_tree = 1;
	  union_groups (e->src, e->dest);
	}
    }

  /* And now the rest.  */
  for (i = 0; i < num_edges; i++)
    {
      edge e = INDEX_EDGE (el, i);
      if (find_group (e->src) != find_group (e->dest)
	  && !EDGE_INFO (e)->ignore)
	{
	  EDGE_INFO (e)->on_tree = 1;
	  union_groups (e->src, e->dest);
	}
    }
}

/* Perform file-level initialization for branch-prob processing.  */

void
init_branch_prob (filename)
  const char *filename;
{
  long len;
  int i;

  if (flag_test_coverage)
    {
      int len = strlen (filename);
      char *data_file, *bbg_file_name;

      /* Open an output file for the basic block/line number map.  */
      data_file = (char *) alloca (len + 4);
      strcpy (data_file, filename);
      strip_off_ending (data_file, len);
      strcat (data_file, ".bb");
      if ((bb_file = fopen (data_file, "wb")) == 0)
	pfatal_with_name (data_file);

      /* Open an output file for the program flow graph.  */
      bbg_file_name = (char *) alloca (len + 5);
      strcpy (bbg_file_name, filename);
      strip_off_ending (bbg_file_name, len);
      strcat (bbg_file_name, ".bbg");
      if ((bbg_file = fopen (bbg_file_name, "wb")) == 0)
	pfatal_with_name (bbg_file_name);

      /* Initialize to zero, to ensure that the first file name will be
	 written to the .bb file.  */
      last_bb_file_name = 0;
    }

  if (flag_branch_probabilities)
    {
      char *da_file_name;

      len = strlen (filename);
      da_file_name = (char *) alloca (len + 4);
      strcpy (da_file_name, filename);
      strip_off_ending (da_file_name, len);
      strcat (da_file_name, ".da");
      if ((da_file = fopen (da_file_name, "rb")) == 0)
	warning ("file %s not found, execution counts assumed to be zero.",
		 da_file_name);

      /* The first word in the .da file gives the number of instrumented
	 edges, which is not needed for our purposes.  */

      if (da_file)
	__read_long (&len, da_file, 8);
    }

  if (profile_arc_flag)
    init_edge_profiler ();

  total_num_blocks = 0;
  total_num_edges = 0;
  total_num_edges_instrumented = 0;
  total_num_blocks_created = 0;
  total_num_passes = 0;
  total_num_times_called = 0;
  total_num_branches = 0;
  total_num_never_executed = 0;
  for (i = 0; i < 20; i++)
    total_hist_br_prob[i] = 0;
}

/* Performs file-level cleanup after branch-prob processing
   is completed.  */

void
end_branch_prob ()
{
  if (flag_test_coverage)
    {
      fclose (bb_file);
      fclose (bbg_file);
    }

  if (flag_branch_probabilities)
    {
      if (da_file)
	{
	  long temp;
	  /* This seems slightly dangerous, as it presumes the EOF
	     flag will not be set until an attempt is made to read
	     past the end of the file. */
	  if (feof (da_file))
	    warning (".da file contents exhausted too early\n");
	  /* Should be at end of file now.  */
	  if (__read_long (&temp, da_file, 8) == 0)
	    warning (".da file contents not exhausted\n");
	  fclose (da_file);
	}
    }

  if (rtl_dump_file)
    {
      fprintf (rtl_dump_file, "\n");
      fprintf (rtl_dump_file, "Total number of blocks: %d\n",
	       total_num_blocks);
      fprintf (rtl_dump_file, "Total number of edges: %d\n", total_num_edges);
      fprintf (rtl_dump_file, "Total number of instrumented edges: %d\n",
	       total_num_edges_instrumented);
      fprintf (rtl_dump_file, "Total number of blocks created: %d\n",
	       total_num_blocks_created);
      fprintf (rtl_dump_file, "Total number of graph solution passes: %d\n",
	       total_num_passes);
      if (total_num_times_called != 0)
	fprintf (rtl_dump_file, "Average number of graph solution passes: %d\n",
		 (total_num_passes + (total_num_times_called  >> 1))
		 / total_num_times_called);
      fprintf (rtl_dump_file, "Total number of branches: %d\n",
	       total_num_branches);
      fprintf (rtl_dump_file, "Total number of branches never executed: %d\n",
	       total_num_never_executed);
      if (total_num_branches)
	{
	  int i;

	  for (i = 0; i < 10; i++)
	    fprintf (rtl_dump_file, "%d%% branches in range %d-%d%%\n",
		     (total_hist_br_prob[i] + total_hist_br_prob[19-i]) * 100
		     / total_num_branches, 5*i, 5*i+5);
	}
    }
}

/* The label used by the edge profiling code.  */

static rtx profiler_label;

/* Initialize the profiler_label.  */

static void
init_edge_profiler ()
{
  /* Generate and save a copy of this so it can be shared.  */
  char *name = ggc_alloc_string (NULL, 20);
  ASM_GENERATE_INTERNAL_LABEL (name, "LPBX", 2);
  profiler_label = gen_rtx_SYMBOL_REF (Pmode, name);
  ggc_add_rtx_root (&profiler_label, 1);
}

/* Output instructions as RTL to increment the edge execution count.  */

static rtx
gen_edge_profiler (edgeno)
     int edgeno;
{
  enum machine_mode mode = mode_for_size (LONG_TYPE_SIZE, MODE_INT, 0);
  rtx mem_ref, tmp;
  rtx sequence;

  start_sequence ();

  tmp = force_reg (Pmode, profiler_label);
  tmp = plus_constant (tmp, LONG_TYPE_SIZE / BITS_PER_UNIT * edgeno);
  mem_ref = validize_mem (gen_rtx_MEM (mode, tmp));

  tmp = expand_binop (mode, add_optab, mem_ref, const1_rtx,
		      mem_ref, 0, OPTAB_WIDEN);

  if (tmp != mem_ref)
    emit_move_insn (copy_rtx (mem_ref), tmp);

  sequence = gen_sequence ();
  end_sequence ();
  return sequence;
}

/* Output code for a constructor that will invoke __bb_init_func, if
   this has not already been done. */

void
output_func_start_profiler ()
{
  tree fnname, fndecl;
  char *name;
  const char *cfnname;
  rtx table_address;
  enum machine_mode mode = mode_for_size (LONG_TYPE_SIZE, MODE_INT, 0);
  int save_flag_inline_functions = flag_inline_functions;
  int save_flag_test_coverage = flag_test_coverage;
  int save_profile_arc_flag = profile_arc_flag;
  int save_flag_branch_probabilities = flag_branch_probabilities;

  /* It's either already been output, or we don't need it because we're
     not doing profile-edges. */
  if (! need_func_profiler)
    return;

  need_func_profiler = 0;

  /* Synthesize a constructor function to invoke __bb_init_func with a
     pointer to this object file's profile block. */

  /* Try and make a unique name given the "file function name".

     And no, I don't like this either. */

  fnname = get_file_function_name ('I');
  cfnname = IDENTIFIER_POINTER (fnname);
  name = xmalloc (strlen (cfnname) + 5);
  sprintf (name, "%sGCOV",cfnname);
  fnname = get_identifier (name);
  free (name);

  fndecl = build_decl (FUNCTION_DECL, fnname,
		       build_function_type (void_type_node, NULL_TREE));
  DECL_EXTERNAL (fndecl) = 0;

#if defined(ASM_OUTPUT_CONSTRUCTOR) && defined(ASM_OUTPUT_DESTRUCTOR)
  /* It can be a static function as long as collect2 does not have
     to scan the object file to find its ctor/dtor routine.  */
  TREE_PUBLIC (fndecl) = 0;
#else
  TREE_PUBLIC (fndecl) = 1;
#endif

  DECL_ASSEMBLER_NAME (fndecl) = fnname;
  DECL_RESULT (fndecl) = build_decl (RESULT_DECL, NULL_TREE, void_type_node);

  fndecl = pushdecl (fndecl);
  rest_of_decl_compilation (fndecl, 0, 1, 0);
  announce_function (fndecl);
  current_function_decl = fndecl;
  DECL_INITIAL (fndecl) = error_mark_node;
  temporary_allocation ();
  make_function_rtl (fndecl);
  init_function_start (fndecl, input_filename, lineno);
  pushlevel (0);
  expand_function_start (fndecl, 0);

  /* Actually generate the code to call __bb_init_func. */
  name = ggc_alloc_string (NULL, 20);
  ASM_GENERATE_INTERNAL_LABEL (name, "LPBX", 0);
  table_address = force_reg (Pmode, gen_rtx_SYMBOL_REF (Pmode, name));
  emit_library_call (gen_rtx_SYMBOL_REF 
		     (Pmode, ggc_alloc_string ("__bb_init_func", 14)), 0,
		     mode, 1, table_address, Pmode);

  expand_function_end (input_filename, lineno, 0);
  poplevel (1, 0, 1);

  /* Since fndecl isn't in the list of globals, it would never be emitted
     when it's considered to be 'safe' for inlining, so turn off
     flag_inline_functions.  */
  flag_inline_functions = 0;

  /* Don't instrument the function that turns on instrumentation.  Which
     is also handy since we'd get silly warnings about not consuming all
     of our da_file input.  */
  flag_test_coverage = 0;
  profile_arc_flag = 0;
  flag_branch_probabilities = 0;

  rest_of_compilation (fndecl);

  /* Reset flag_inline_functions to its original value.  */
  flag_inline_functions = save_flag_inline_functions;
  flag_test_coverage = save_flag_test_coverage;
  profile_arc_flag = save_profile_arc_flag;
  flag_branch_probabilities = save_flag_branch_probabilities;

  if (! quiet_flag)
    fflush (asm_out_file);
  current_function_decl = NULL_TREE;

  assemble_constructor (IDENTIFIER_POINTER (DECL_NAME (fndecl)));
}